There exists a plurality of methods for the application of a coating of a viscous homogeneous layer to a substrate. The main methods are based on dipping, use of a roller mechanism spraying or the like. In some of the cases excess has to be removed: the removal by means of a squeezer system also increases the homogeneity of the layer. The material is generally in a fluid state and is converted to a "frozen solid" after application. When coating of the order of 0.01 mm or less is required, there must be adhered to very stringent controls of each feature of the coating step: such coatings are generally applied in special coating facilities.
Coatings such as adhesives are applied by means of a solid applicator which is coated with a viscous material, which applicator is contacted with the substrate. Such means cannot be used with film emulsions which ought hot to be touched by anything but the developer.
Polaroid-type film development systems provide a package of a predetermined quantity of development agent for use with each individual film and means for evenly spreading this on such film. The Polaroid system is expensive due to the separate containers for each development dosage for individual films and this system is not flexible as the developer quantity is intended for a given film size only. This system cannot be used for large film sizes.